INDUSTRIAL AND ENGINEERING CHEMISTRY
March 15,1934
Typical results obtained on some low-grade rosins by this proposed method are shown in Table I.
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method. The acid number can therefore be reported to the first decimal place.
SUMMARY
TABLEI. TYPICALRESULTSONILOW-GRADE ROSINS SAMPLBSAMPLESAMPLESAMPLESAMPLB
Individual determinations
1' 2a FF wood B gum 151.6 161.5 151.3 161.5
ii::: i::
With the aid of a direct-vision hand spectroscope for observing the end point, the acid number of the lowest grade (reddest) rosin can be determined with a degree of i,"!::: accuracy equal to that ordinarily obtained with high-grade 157.1 or yellow rosin.
3 4 5 B gum D gum E gum 156.0a 161.0a 157.2a 156.3" i61.3a 157.2a
Average acid number 151.4 161.4 166.0 a Determinations made on 5-gram portions. b Determinations made on 5.5-gram portions. 0 Determinations made on 4.5-gram portions.
::;::: 161.0
The probable error in titration by this method is not greater than 0.1 cc. of 0.5 N alkali, corresponding to an error of less than 0.6 in acid number when a &gram sample is used, This is equal to the accuracy ordinarily obtained in titrating a 1- to 2-gram sample of high-grade rosin by the conventional
LITERATURE CITED (1) Brice, Naval Stores Rev., 43, No. 30 (Oct. 21, 1933); Drugs, Oils & Paints, 48,380 (1933). (2) Brode, J. Am. Chsm. SOC.,46,581 (1924). (3) Coburn, IND.ENQ.CHEM.,Anal. Ed., 2, 181 (1930). IND. ENQ. CHEM*,20, 423 (1928). (4) Mfiller and RECEIVED October 31, 1933.
Quantitative Estimation of Furfural at 0" C. with Bromine ELIZABETH E. HUGHES AND S. F. ACREE,Bureau of Standards, Washington, D, C. HE quantitative estimation of pentoses and pentosans
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is often required in the work of agricultural experiment stations, medical research laboratories, paper mills, and rayon and textile plants. The usual procedure involves the distillation of the material with hydrochloric acid to convert the pentose derivatives into furfural, which is then determined in the distillate. Among the best known reagents for this latter purpose are phloroglucinol, thiobarbituric acid, and dinitrophenylhydrazine used gravimetrically, and bromine or bromate used volumetrically, The amount of bromine taken up by the furfural has been estimated by electrometric titration by Pervier and Gortner (6),Kline and Acree (S),Magistad (4),and others, and with an excess of bromine and back-titration with potassium iodide and thiosulfate by van Eck ( I ) , Powell and Whittaker (8),Kline and Acree (S),and others. The gravimetric methods, especially with thiobarbituric acid, require a t least 24 hours and involve the usual difficulties in filtering and weighing. The present volumetric methods are more rapid but less accurate when performed a t room temperature. This is due to the fact that the rapid consumption of one mole of bromine per mole of furfural is followed by the slow addition of a second mole of bromine a t 20" to 30" C. The large temperature coefficient of the second reaction observed by Magistad (4) and the authors introduces considerable error when determinations are made a t variable room temperatures. Furthermore, it is found that considerably more than two molecules of bromine react with furfural a t 20" to 30" C. when the reaction time is prolonged. The authors have, therefore, carried out a series of experiments on the reaction of bromine and furfural at 0" C. to determine whether the reaction could be limited to the first rapid step a t this low temperature.
EXPERIMENTAL The furfural was extracted with alkali to remove acid and fractionated under reduced pressure. It had a boiling point of 161.6" C. at 760 mm. Freshly distilled furfural was sealed in small glass balloons holding about 1 gram, and weighed. They were placed under water in graduated flasks and crushed, the flask was filled t o the mark with water, and samples were pipetted into special Erlenmeyer flasks containing 200 ml. of 3 per cent hydrochloric acid. The 3 per cent hydrochloric
acid was used because it is rarely exceeded in the usual furfural distillates and liberates the bromine fully. The hydrochloric acid in 6 to 12 per cent concentrations (3,6, 6) decomposes the added thiosulfate. As it is very difficult to prevent the escape of bromine when standard 0.1 N potassium bromate plus potassium bromide is added t o acidified furfural in open vessels, groundglass-stoppered Pyrex Erlenmeyer flasks were fitted with two side arms t o hold measured volumes of 0.1 N potassium bromate plus potassium bromide and of 10 per cent potassium iodide solution. To prevent accidental tilting and mixing, lead horseshoes were placed around the bottoms of the flasks, which were suspended from the edge of the ice bath with heavy wires fastened about the necks. The flasks were cooled between 0' and 2" C. in an ice and water bath and the reaction started by tilting the flask to allow the bromate solution t o run into the furfural. The solutions were mixed and allowed t o stand until it was desired t o stop the reaction, when 10 ml. of 10 per cent potassium iodide in the other side arm was run into the mixture. The flask was removed from the ice bath and shaken vigorously to allow the enclosed bromine gas to react with the potassium iodide. The stopper was removed, rinsed as usual, and the contents were titrated with 0.1 N thiosulfate by using starch indicator. Under the appropriate conditions one mole of furfural reacts with one mole of bromine; hence one ml. of 0.1 N thiosulfate or 0.1 N potassium bromate is equivalent to 0.0048 gram of furfural.
TABLBI. REACTION OF BROMINE WITH FURFURAL AT o o C REACTION TIME Min. 10 sec. (approx.) 1 (approx.) 2 3 4 5 6 7 8 10 30
eo
90 240
PERCENTOB THEORETICAL AMOVNT OB FURFURAL FOUND 100-mg. 57-mg. 45-mg. 10-mg. sample
sample
sample
samplsO
%
%
%
% ... ...
... ...
... ... ... ... ...
99.6 99.5 100.0 100.2 100.3 100.1 100.1 100.4 iOi:3 103.0
... ...
... ... 1oo:o 99.9 99.7
...
99.8
31.5 99.3 100.1 100.2 100.0
...
99.1 100.0 100* 9 100 5
... ... ... 99.6 ... ...
... ... ... ... ...
100:3
100:3 100.1 101.8 103.0 105.5
16615
l00:5
1oi:0
ioi:4 102.6
...
... ...
... ...
...
103.4
iii.*s
... ...
a With small samples which use u p only 2 ml. the titration error is neoensarily large. 0.5 drop, or 0.02 ml. represents 1 per cent. This acoountn for the larger variations in the percentages.
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ANALYTICAL EDITION
In the experiments given in Table I, 25 ml. of 0.1 N potassium bromate containing 50 grams of potassium bromide per liter were used. This quantity of potassium bromate is suitable for samples containing from 10 to 100 mg. of furfural. The results show clearly that a t 0" C. and within about 3 to 10 minutes only one mole of bromine reacts with the furfural. The use of specially constructed Erlenmeyer flasks eliminates the loss of bromine during the reaction. This is shown by the fact that the blanks run on the reagents standing as long as one hour checked within 0.1 per cent. As a further precaution against the loss of bromine it is advisable to seal the ground-glass joint with sirupy phosphoric acid. The presence of direct sunlight should be avoided during the reaction, but no evidence of marked photochemical influence was observed under laboratory conditions in check experiments run in diffused light or in the absence of light. Comparative studies a t O", 5", lo", 21" C., and higher on both furfural and furoic acid indicate that the end point can be more quickly and accurately ascertained for the reaction of furfural with one molecule of bromine a t 0" C. than with two molecules a t higher temperatures. As furoic acid reacts very rapidly with more than one molecule of bromine under these conditions, it is suggested that furfural is converted
Vol. 6, No. 2
first into a bromo derivative such as 4,5-dibromo-2-furfural
($1. CONCLUSION
A method is given for the quantitative estimation of furfural by treating it 5 minutes a t 0" C. with an excess of 0.1 N potassium bromate plus potassium bromide in 3 per cent hydrochloric acid and determining the unused bromine with potassium iodide and 0.1 N thiosulfate. The furfural combines with one mole of bromine. LITERATURE CITED (1) Eok, P. N. van, Verslag. v. d. Verricht. v. h. Centr. lab. v. d. Volksgerondheid, (1918); Chem. A h . , 14, 509 (1920). (2) Gilman and Wright, J . Am. Chem. Soc., 52, 1170 (1930). (3) Kline, G. M., and Acree, S. F., B u r . Standards J . Research, 8, 25 (1932). (4) Magistad, 0. C., IND. ENG.CHEM.,Anal. Ed., 5, 253 (1933). (5) Pervier, N. C., and Gortner, R. A,, IND. ENG.CHEM.,15, 1167, 1255 (1923). (6) Powell, W. J., and Whittaker, H., J . Soc. Chem. I n d . , 43, 35T (1924). RBCEIVED December 5, 1933. Publioation approved by the Director of the Bureau of Standards, U. S. Department of Cornmeroe.
A Study of Synthetic Cryolite Analysis F. J. FRERE, Pennsylvania Salt Manufacturing Company, Philadelphia, Pa.
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HE chief distinction between natural cryolite (Kryolith) and synthetic cryolite lies in the fact that all the constituents of the natural variety are combined in a definite chemical ratio and that this salt always occurs as an individual and never as a mixture. Therefore, in order to determine its purity it is necessary only to make a single determination of any one constituent. On the other hand, synthetic cryolite usually contains other compounds such as sodium fluoride, aluminum fluoride, and occasionally aluminum oxide, which may vary over a wide range, depending to a great extent upon the method of preparation. In view of the great differences which exist between these two products, an analytical procedure for the determination of each component in synthetic cryolite becomes highly desirable. The primary purpose of this investigation, however, has not been to set forth any definite analytical procedure, but rather to point out the differences between the two products, to identify some of the chief components, and to test the applicability of certain procedures which may ultimately lead to an acceptable method of analysis.
fluoride concentrations was calculated. The results of these experiments are given in Table I. TABLEI. SOLUBILITY O F NATURAL CRYOLITE IN SOLUTIONS OF SODIUM FLUORIDE NaF ADDED NaaAlFe FOUND NaF ADDED Gram/lOO ml. 0.0
0.006 0.015 0.025
Grarn/lOO ml.
0.0345 0.0263 0.0176 0.0059
Gram/lOO ml.
0.035 0.050 0.075 0.100
AQUEOUS
NasAlFs FOUND Gram/lOO ml. 0.0020 0.0011 0 . OOOb 0.0000
DETERMINATION OF SODIUM FLUORIDE The possibility of a procedure for the direct estimation of sodium fluoride seems rather remote, owing to the lack of a suitable solvent in which sodium fluoride is alone soluble. As a result, an indirect procedure based on the insolubility of cryolite in the presence of sodium fluoride has been developed, which succeeds only in the absence of soluble or reactable aluminum salts. Since aluminum fluoride is completely insoluble, its presence causes no interference. PROCEDURE. Weigh out 5 grams of the sample and transfer to a 500-ml. volumetric flask. Add about 250 ml. of water and a itate vigorously for about 0.5 hour t o insure complete solution SOLUB~LITY I N AQUEOUS SOLUTIONS OF SODIUM FLUORIDE o f the sodium fluoride. Add a sufficient quantity of a known As a basis for a possible quantitative estimation of sodium solution of sodium fluoride t o give this salt a concentration of fluoride, the solubility of cryolite in aqueous solutions of this about 0.10 gram per 100 ml. Make up to volume, mix thoroughly by shaking, and filter on a dry funnel. Transfer 100 ml. of the salt was determined. solution t o a 250-ml. beaker and make exactly neutral to phenolAdd a few drops of methyl red and titrate with a Samples of natural cryolite to which were added known varied phthalein. amounts of sodium fluoride were made up to a definite volume, standard solution of yttrium nitrate. The sodium fluoride added subtracted from that found represents the amount present in the stoppered tightly, and allowed to remain at room temperature (approximately 25" C.) for one week. Approximately a tenfold original sample. excess of cryolite was used to insure saturation. The flasks were In order to ascertain the applicability of such a procedure, shaken at frequent intervals in order that equilibrium might be established as com letely as possible. At the end of this period, synthetic mixtures were prepared from pure materials and the filtered portions o?each solution were treated with about 10 ml. sodium fluoride was determined. The fluorine was deterof perchloric acid and the fluorine was expelled by evaporating mined by means of yttrium nitrate as outlined by the author t o fumes in a platinum dish. The aluminum in the residues (3) in a previous article. The results of these experiments are was determined by means of 8-hydroxyquinoline and from the amount found the solubility of cryolite at the various sodium given in Table 11.
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